1. Field of the Invention
The present invention relates to boats, and particularly to a bow or stern thruster for commercial boats, such as fishing boats, ferries, etc., as well as for large yachts, which provides a propulsion means for steering the boat in docking maneuvers, or for maintaining the boat's position against strong winds and/or current, commonly called "dynamic positioning. The thrusters also allow barges to make tighter turns in rivers.
2. Description of the Related Art
Some boats or vessels are equipped with a bow or stern thruster as a supplemental means of propulsion for steering purposes, since the boat's response to the rudder may be slow. The conventional thruster comprises either a single or double screw propeller disposed in a tunnel aligned transversely through either the bow or the stern of the vessel. In constructing a bow or stern thruster, it is advantageous to construct the tunnel with as small a diameter as possible. The small diameter has the advantage of: reducing the dead load caused by the volume of water which fills the tunnel, thereby improving fuel economy; since the diameter of the tunnel is smaller, the aft wall of the tunnel presents a smaller resistance to the flow of water when the vessel is in motion; allows placement further forward in the hull, increasing the moment arm produced by the thruster, reducing tunnel length which further reduces the dead load; allows placement in shallow draft vessels; requires less submergence; and allows the tunnel to fit in vessels which have narrowly spaced structural ribs in the hull without the necessity for expensive structural alterations in the hull.
This object may be achieved by developing the maximum horsepower attainable in the smallest practicable drive mechanism. The amount of horsepower developed depends upon the size of the gears used to transmit power from the drive shaft to the propeller shafts. Generally, the larger the gear, the larger the horsepower developed to steer the vessel, but larger gears sizes have also required larger gearbox housings and larger tunnels.
The efficiency of the bow or stern thruster may also be improved by providing a gearbox and its supporting apparatus with a narrow profile to present less resistance to the flow of water through the tunnel, effectively increasing water flow without increasing tunnel size.
A further consideration involves the necessity for maintenance on the thruster unit. Conventional thruster gear box units have a shaft extending from one or both sides of the gearbox housing on which propeller hubs may be mounted. Thruster units, as with all machinery, require oiling or lubrication from time to time, and being exposed to the water, they may requiring painting as protection from corrosion periodically. Conventional gearbox construction may require drydocking for a week or more in order to perform maintenance services. A gearbox design allowing removal of the thruster unit from the tunnel while the boat is still in the water would be desirable.
A variety of bow or stern thruster devices and related propulsion devices are known in the art. U.S. Pat. No. 598,424, issued Feb. 1, 1898 to W. Kuss, describes a pair of propellers mounted on a shaft in a passage extending transversely across the ship. The propeller shaft is driven by a drive shaft coupled to the crankshaft of the main engine by bevel gearing. U.S. Pat. No. 1,288,106, issued Dec. 17, 1918 to F. V. Medynski, discloses an arcuate tube extending across the stern of a vessel, a motor in the engine room being situated in the bend of the tubing and being coupled to shafts extending in opposite directions through packing glands in the walls of the tube. Propellers are mounted on the ends of the shafts, the shafts being supported by bearings suspended from the walls of the tube by radial arms.
U.S. Pat. No. 2,699,138, issued Jan. 11, 1955 to H. B. Dyer, teaches a steering apparatus for a barge having a vertical housing extending from the deck through the skeg of the barge, the housing having a transverse port in which a gearbox with a single propeller is disposed. U.S. Pat. No. 3,127,865, issued Apr. 7, 1964 to F. W. Pleuger, shows a propulsion unit in a transverse duct in the bow of a vessel in which tandem propellers are operated at different speeds by a differential. U.S. Pat. No. 3,185,122, issued May 25, 1965, also to Pleuger, shows a streamlined casing mounted in a tube extending transversely through the ship, the casing being supported by hollow struts, the casing housing propeller shafts driven by a chain and sprocket assembly, the chain being partially disposed in the hollow struts.
U.S. Pat. No. 3,550,547, issued Dec. 29, 1970 to Pleuger, et al., teaches a bow thruster which may be used for main propulsion when the main engine is damaged. The thruster is mounted in a tube which is used for steering when retracted, but which may be extended below the ship and rotated in any direction to drive the ship. U.S. Pat. No. 3,970,027, issued Jul. 20, 1976 to W. M. Jackson, describes a device for "priming" bow steering pumps in barges. A filter pump drives a shaft with dual propellers disposed in a tube extending transversely through the bow and sloping downwards at the sides to form nozzles. The devices includes a vacuum pump and tubing with air and water inlets to overcome the vacuum effect caused by water rushing out the nozzle. U.S. Pat. No. 4,074,652, issued Feb. 21, 1978, also to Jackson, shows a transverse tube mounted on a rotatable shaft for steering a barge in any direction.
U.S. Pat. No. 3,903,833, issued Sep. 9, 1975 to Lais et al., shows a propulsion device for shallow draft vessels having a trough in the stern. The device has a vertically mounted propeller which draws water upward and out through elbow shaped tunnels at the sides. U.S. Pat. No. 3,918,389, issued Nov. 11, 1975 to K. Shima, discloses a turbine propulsion device with a worm wheel connected to a steering device. U.S. Pat. No. 4,147,125, issued Apr. 3, 1979 to O. G. Slade, teaches propulsion machinery mounted vertically in the hull which takes water in and expels it in a jet to propel the vessel. Steering is accomplished by ring and pinion gears which direct output baffles as desired.
U.S. Pat. No. 4,175,511, issued to F. Krautkremer, describes; propulsion machinery for tugboats which includes twin propellers on separate shafts with separate drive machinery, the propellers extending below the hull and being rotatable through 360.degree.. U.S. Pat. No. 4,278,431, issued Jul. 14, 1981 to Krautkremer, et al., shows a hydro-jet propulsion device for flat-bottomed watercraft having a rotatable tube with an elbow shape, a propeller eccentrically mounted in the input port of the elbow, the input and output ports being on the bottom of the watercraft.
U.S. Pat. No. 4,411,630, issued Oct. 25, 1983, also to Krautkremer, et al., shows an improvement to the '431 device which includes a port and passage for air into the outlet leg of the elbow in order to drive the water jet downward instead of allowing it to flow under and parallel to the hull. U.S. Pat. No. 4,412,500, issued Nov. 1, 1983, also to Krautkremer, shows an arrangement for controlling the speed of a bow or stern thruster driven by a hydraulic motor mechanically linked to the main engine which uses a feedback circuit to control the speed of the hydraulic motor.
U.S. Pat. No. 4,419,082, issued Dec. 6, 1983 to Krautkremer, et al., teaches a water-jet drive mechanism for driving and controlling a shallow draft vessel which has a cylindrical housing containing a centrifugal pump with a spiral housing, the pump being inclined at an angle. U.S. Pat. No. 4,838,821, issued Jun. 13, 1989, also to Krautkremer, improves the '082 device by a ring connecting the blades of the pump to prevent damage to the blades of the pump in lieu of a screen.
U.S. Pat. No. 5,146,865, issued Sep. 15, 1992 to Lais, et al. describes a pot-pump propulsion system for flat bottom boats. U.S. Pat. No. 5,336,119, issued Aug. 9, 1994, also to Lais, et al., teaches a low emission drive unit for light watercraft using an electric motor to drive a belt-driven propeller shaft.
U.K. Patent No. 1,130,378, published Oct. 16, 1968, shows a bow thruster with transverse inlet tubes feeding a vertical shaft having a venturi tube leading to an impeller and narrowing to a nozzle. The nozzle emits a jet transversely. In a retracted position, the nozzle may eject to either side for low speed maneuvering. The nozzle may also be extended below the keel and rotated 360.degree. for maneuvering on the open sea. U.K. Patent No. 1,189,779, published Apr. 29, 1970, shows a bow thruster mounted in a tube transverse to the axis of the vessel with an impeller driven by an electric motor through bevel gearing, the outlet of the impeller being narrowed to form a nozzle emitting a jet. The impeller is supported by vanes and has a wide nose on the inlet side and a bullet shape on the outlet side. The device includes a worm gear to rotate the impeller 180.degree. to change the direction of thrust.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a bow or stern thruster solving the aforementioned problems is desired.